In particular, the present invention is concerned with the effective use of a manganese complex as catalyst for the bleach activation of peroxy compound bleaches.
Peroxide bleaching agents for use in laundering have been known for many years. Such agents are effective in removing stains, such as tea, fruit and wine stains, from clothing at or near boiling temperatures. The efficacy of peroxide bleaching agents drops off sharply at temperatures below 60.degree. C.
It is known that many transition metal ions, including manganese ions, catalyze the decomposition of H.sub.2 O.sub.2 and H.sub.2 O.sub.2 -liberating percompounds, such as sodium perborate. It has also been suggested that transition metal salts together with a co-ordinating ligand (i.e. a chelating agent) can be used to activate peroxide compounds so as to make them usable for satisfactory bleaching at lower temperatures. Not all combinations of transition metals with ligands appeared to be suitable for improving the bleaching performance of peroxide compound bleaches.
Many combinations indeed show no effect, or even a worsening effect, on the bleaching performance; no proper rule seems to exist by which the effect of metal ion/ligand combinations on the bleaching performance of peroxide compound bleaches can be predicted.
Various attempts have been made to select suitable metal/chelating agent combinations for said purpose and to correlate bleach-catalyzing effect with some physical constants of the combination; so far without much success and of no practical value.
U.S. Pat. No. 3,156,654 suggested transition metals, though particularly cobalt andcopper salts, in conjunction with pyridine-2-carboxylic acid or pyridine-2,6-dicarboxylic acid, preferably as a preformed complex, as being a suitable combination. Another suggestion is made in U.S. Pat. No. 3,532,634 to use a transition metal salt, together with a chelating agent in combination with a persalt and an organic bleach activator. It is said here that the chelating agent should have a first complex formation constant with the transition metal ion of log 2 to about log 10 at 20.degree. C. Preferred options include (di)-picolinic acid, pyrrolidine-carboxylic acids and 1,10-phenanthroline, whereas well-known chelating agents, such as ethylene diamine tetraacetic acid--found usable according to U.S. Pat. No 3,156,654 --are unsuitable.
Other patent documents discussing the combined use of ligands or chelating agents with manganese are, for example, EP-A-0072166 and EP-A-0141470, which suggested the use of pre-complexed manganese cation with specific chelating agents, particularly of the class of (poly)amino polycarboxylates.
All these prior art suggestions are based on systems in which free metal ion is the catalytically active species and consequently produce results in practice that are often very inconsistent and/or unsatisfactory, especially when used for washing at low temperatures.
For a transition metal in general and manganese in particular to be useful as a bleach catalyst in a detergent bleach composition, the transition metal, i.e. manganese, must not unduly promote peroxide decomposition by non-bleaching pathways and must be hydrolytically and oxidatively stable. The first requirement is with respect to the often dark-colored metal (hydr)oxide formation, the second requirement, for example, upon addition of hypochlorite or other oxidants.
U.S. Pat. No 4,728,455 discusses the use of catalysts for peroxide bleach based on a combination of Mn(III) and the hydroxycarboxylic acids that can form complexes at the preferred Mn-to-ligand ratios which are stable with respect to hydrolysis and oxidation. An example of this type of catalyst is Mn(III)-gluconate. Although a large series of hydroxyl-containing compounds is claimed, at least one carboxylic acid group or its salt is always present in the ligands.
The importance of the carboxylate group to obtain stable metal complexes with these types of ligands was furthermore suggested by M. van Duin et al; the carboxylate group functions as a promoter of the acidity of the hydroxyl proton of the OH-group adjacent to the carboxylate group, thereby improving participation in the co-ordination of the metal ion. [M. van Duin, J.A. Peters, A.P.G. Kieboom and H. van Bekkum, Recueil de Travaux chimiques des Pays-Bas, 108/2, Feb. 1989].
The above-mentioned patent and scientific literature strongly suggests that the carboxylate group be an essential part of the ligand to obtain stable complexes.